Mounjaro

Mounjaro works through two hormone pathways - glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) - that signals to your brain that you are full. Most weight loss injections work on one pathway. Mounjaro works on both. ^[4]

In practical terms this means:

• Reduced appetite: you feel less driven to eat between meals
• Less food noise: cravings become easier to manage
• Feeling fuller for longer: meals feel more satisfying, even smaller ones
• Steadier blood sugar: fewer hunger spikes throughout the day

Mounjaro works best alongside healthy eating and regular physical activity, with ongoing support from your clinical team.

Initially approved for type 2 diabetes but is also effective for weight loss. It has been approved for obesity treatment in some countries, including the UK.

Mounjaro starts working from your first dose. Most people notice a reduction in appetite and cravings within the first week. Visible changes to your weight tend to follow over the coming months, and results continue to build throughout treatment. Noticeable changes become more apparent at around month 3.

Weight loss is not always reflected immediately on the scales. How your clothes fit and how you feel are equally - if not more - useful measures of progress. Everyone responds slightly differently, and your prescriber will monitor your progress and adjust your dose when needed.

Weight loss outcomes depend on factors such as dose, diet, and exercise. Some people may experience slower weight loss initially before reaching a higher dose.

There is a reduced BMI threshold for some ethnic groups due to higher health risks associated with weight.

These groups include individuals from South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean heritage. ^[9]

You can quickly calculate your Body Mass Index.

This medication is not suitable for everyone.

You should not use it if you are:

• Under 18 or over 85
• Pregnant or breastfeeding
• Allergic to any of its ingredients

You may also be unable to use it if you ^[4]:

• Have severe kidney or liver problems
• Have a history of pancreatitis or gallstones
• Have severe gastrointestinal disease
• Currently take other medications that lower blood sugar levels

If any of these apply to you, please discuss your options with a healthcare professional before starting treatment.

Most patients find the Mounjaro weight loss injection straightforward once they understand the steps. Your prescriber or pharmacist can walk you through use before treatment starts, and injections usually become easier with practice.

CONTENT REQUIRED HERE

The standard titration schedule is:

Your prescriber will increase your dose in 2.5mg steps every 4 weeks, only when needed. Each dose increase is guided by how you are responding to treatment.

The lower strengths of Mounjaro 2.5 and 5mg will not achieve the best results. While some weight loss will be observed, the primary function of these doses is to help your body adjust to the drug without experiencing serious side effects.

For a full breakdown of how dosing works and what to expect at each stage, read our Mounjaro dosage and maintenance guide.

If you miss a dose of Mounjaro, what you do next depends on how much time has passed ^[4]:

• Within 4 days of your missed dose - take it as soon as possible
• More than 4 days have passed - skip the missed dose entirely
• Take your next dose on your usual day
• Never take a double dose

Mounjaro is a once-weekly injection. Best taken on the same day and time once every week.

Mounjaro is injected once a week, on the same day each week, at any time of day, with or without food.

1. 1
   Wash your hands with soap and water to ensure cleanliness.
2. 2
   Inspect the pen before use:

   • Check the expiration date
   • Look for any visible damage
   • Verify the medication appears clear and colourless
3. 3
   Attach a new needle to the pen, ensuring it's firmly secured.
4. 4
   Prime the pen:

   • Turn the dose knob slowly until you hear 2 clicks
   • Point the needle upward
   • Press the dose knob to release any air bubbles and confirm the pen is working
5. 5
   Set your dose:

   • Turn the dose knob to your prescribed dosage (typically starting at 2.5 mg, increasing as directed by your healthcare provider)
   • Listen for clicks to confirm the correct dose is selected
6. 6
   Choose and prepare the injection site:

   • Common sites: abdomen, thigh, or upper arm
   • Rotate sites to avoid irritation
   • Pinch the skin gently if preferred
7. 7
   Inject the medication:

   • Insert the needle at a 90-degree angle into the skin
   • Press down the dose knob firmly
   • Count slowly to 5 while keeping the needle in place
8. 8
   Withdraw and verify:

   • Pull the needle straight out of the skin
   • Check that the dose counter returns to 0
   • Apply gentle pressure with a tissue if needed
9. 9
   Secure the pen:

   • Remove the needle from the pen and place in sharps bin
   • Replace the pen cap
   • Store the pen as directed (typically in the refrigerator)

CONTENT REQUIRED HERE

• Injection site reactions such as bruising, pain or a rash

CONTENT REQUIRED HERE

The most common side effects of Mounjaro are ^[4]:

• Nausea
• Diarrhoea
• Vomiting
• Constipation
• Indigestion
• Stomach pain
• Bloating
• Burping
• Flatulence
• Headaches

These are most noticeable during the first few weeks and after each dose increase. Starting on a low dose and increasing gradually helps reduce their impact.

Other common side effect are ^[4]:

• Dizziness
• Low blood pressure
• Fatigue
• Injection site reactions
• Rash
• Hair loss - usually temporary and more closely related to rapid weight loss than to the medication itself

Persistent nausea, vomiting, or diarrhoea can lead to dehydration. In some cases this can affect kidney function, including in people with no prior kidney problems. ^[4]

Stay well hydrated throughout treatment and tell your prescriber if symptoms are severe or prolonged.

The most common early side effects. For most people it improves within the first few weeks as the body adjusts.

While the following side effects are less common they should not be ignored ^[4]:

Serious risks include pancreatitis, gallbladder issues, and a rare risk of thyroid tumours. Mounjaro is not recommended for individuals with a family history of medullary thyroid cancer.

Mounjaro is under additional safety monitoring in the UK. This means it is a newer medicine and the MHRA is collecting more data on its long-term effects. ^[5] It does not mean it is unsafe - it means it is being watched closely.

Do not use Mounjaro if you ^[4]:

• Are allergic to tirzepatide or any ingredient in the Mounjaro pen
• Have a personal or family history of medullary thyroid carcinoma
• Have Multiple Endocrine Neoplasia syndrome type 2
• Are pregnant or breastfeeding

Speak to your prescriber before starting Mounjaro if you have:

• A history of pancreatitis
• Severe gastrointestinal disease
• Kidney problems
• Diabetic retinopathy

If any of these apply to you, your prescriber will assess whether Mounjaro is appropriate or whether an alternative treatment is more suitable. If you experience a side effect, you can report it directly to the MHRA through the Yellow Card scheme. This helps build a clearer picture of how the medicine performs in real-world use.

Mounjaro can interact with some medicines and supplements. Delayed stomach emptying can affect how some medicines are absorbed, and some combinations can increase risk.

Mounjaro (tirzepatide) slows stomach emptying, which may affect how some oral medicines are absorbed. This is usually not clinically significant, but for medicines requiring stable blood levels (such as warfarin or lithium), closer monitoring may be needed when starting or adjusting treatment. If unsure of potential interactions with your current medication, speak to your doctor or one of our healthcare professionals before starting treatment.

Some medicines can interact with Mounjaro such as:

• Anticoagulants (blood thinning medication) such as warfarin
• Anti-diabetic medication such as sulfonylureas and insulin
• GLP-1 receptor agonists such as Victoza

Mounjaro can be dangerous in certain conditions so it is especially important to mention if you have:

• Heart failure
• Aged 75 years or older
• Severe renal (kidney) disease
• Severe hepatic (liver) disease
• Pancreatitis

Mounjaro does not typically cause low blood sugar unless it is taken in combination with insulin or certain other diabetes medications. If you experience symptoms like dizziness, shakiness, or weakness, seek medical advice.

For a full breakdown of side effects and how to manage them, read our Mounjaro side effects guide.

If you take the oral contraceptive pill, you will need to use additional contraception when starting Mounjaro and after each dose increase.

Mounjaro slows stomach emptying, which can reduce how much of the pill is absorbed and make it less effective.

To maintain reliable contraception, use a barrier method or switch to a non-oral contraceptive for 4 weeks after starting treatment and for 4 weeks after each dose increase. ^[4]

Non-oral methods that are not affected in the same way include:

• The coil
• Implant
• Injection
• Patch
• Vaginal ring

As you lose weight, fertility can increase. Reliable contraception is important throughout treatment. If the contraceptive pill is your preferred method and you do not want to change it, it is worth discussing Wegovy and the contraceptive pill with your prescriber, as it does not carry the same interaction.

Leave one week between your last Wegovy dose and your first Mounjaro dose. Switching from 0.25 mg - 1.7 mg you must start Mounjaro at 2.5mg and retitrate gradually, however if you are switching from 2.4 mg or 7.2 mg you may be able to start on 5 mg of Mounjaro. Your prescriber will advise the best course.

During the washout period you may feel hungrier than usual - this is normal as your body adjusts.

Leave one week between your last Mounjaro dose and your first Wegovy dose. Depending on your current Mounjaro dose, you may not need to start Wegovy at the lowest dose - your prescriber will advise the most appropriate starting point.

For full guidance on both switching routes, read our dedicated articles:

Switching from Mounjaro to Wegovy →

Switching from Wegovy to Mounjaro →

Yes, you can switch from Ozempic to Mounjaro, but you will need to restart at Mounjaro’s lowest dose (2.5 mg) to minimise side effects. Your doctor will guide you through the transition.

Mounjaro is one of several prescription weight loss treatments available in the UK, and it is not always the right starting point for everyone.

Injectable treatments work by reducing appetite and slowing digestion. Mounjaro's dual GIP and GLP-1 action sets it apart from other injectable options, which is reflected in its trial data. But stronger average results do not always mean the right fit for every patient.

For patients who prefer not to inject, weight loss pills offer an alternative route. Orlistat is currently the main licensed weight loss medication available in capsule form in the UK. It works differently to injectable treatments- rather than reducing appetite, it reduces the amount of fat your body absorbs from food.

A thorough assessment is the best way to find the treatment that suits you.